Photographic media and process



media and processes.

Patented June 1 1926.

A UNITEDISTA'TES" PATENT OFF-ICE.

MURRAY C. BEEBE AND ALEXANDER MURRAY, OF CINCINNATI, OHIO, ASSIGNORS TO THE WADSWORTH WATCH CASE COMPANY, OF DAYTON, KENTUCKY, A CORPORA- TION OF KENTUCKY.

rno'rocnnrinc MEDIA AND rnocns's.

No Drawing.

This invention relates to photographic The invention utilizes a. wide range of hydrophobic colloids, in the nature of unsaturated compounds, which are capable of being transformed under the selective action of light transmitted, or projected, in accordance with a luminous image,

In the invention, use is made of sensitizing agents and solvents. The sensitizing agents which are employed in association with the hydrophobic colloids, in accordance with the invention, preferably afford a source of halogen; and by preferdesign or character.

-ence, the sensitizer comprises a halogenliberating compound which is adapted, under the action of light, to liberate halogen which apparently acts as a catalytic agent in effecting the selective transformation of the colloidal body by the selective act-ion of light in accordance with an image, design or character. Also, the solvent medium employed should comprise a solvent, or mixture of.

solv nts, which is capable of dissolving, or holding in suspension, both the hydrophobic colloid and the special sensitizer employed. other characteristics which are desirable in such a. solvent will be noted hereinafter.

According to the present invention, it is possible to utilize unsaturated organic compounds for photographic purposes. These unsaturated organic compounds, as indicated, afford hydrophobic colloids, which may be placed-in solution and applied to suitable surfaces as coatings which are more or less sensitive to light, and are capable of being transformed under the selective action of light; and after such transformation, such coatings,.or films, are capable of being developed, or fixed, in accordance with wellknown methods, and in accordance with methods hereinafter pointed out. The selective action of light may occur by means ofloids herein referred to, accelerating agents.

Application filed January 22, 1923. Serial No. 614,068.

to employ suitable v On the other hand, some of the colloids are so light-sensitive that they may be employed for photographic purposes, without the use of a sensitizing agent. In any case, it isdesirable to employ solvents which will give to the coating, or film,-certa in characteristics as hereinafter more particularlypointed out.

In addition to asphaltum and natural resms,-referred to in a previously filed appli cation, we utilize compounds which are crerivatives of the carbocyclic, heterocyclic, or ali hatic series, of unsaturated compounds; am the invention comprises the use in photography of all and sundry equivalent compounds Which may or may not be light-sensitive, and which may have their sensitivity increased by the addition of cooperating sensitizers.

In the present application, we claim photograpl1ic, media and processes involving the use of a very wide range of hydrophobic colloids, combined with special solvents, with or without the use of special sensitizers.

' In using the term unsaturated compounds we wish to define it in the broadest sense as used in organic chemistry to include not only olefine and acetylene linking in open chain compounds, but also in the rings of cyclic compounds, or between other atoms than carbon atoms in organic compounds such as carbon-oxygen and carbon-nitrogen linkages, etc., without limitations to unsaturated linkage between carbon atoms alone. 1th these and other ends in view, we

herewith describe such instances of adaptabrcad underlying so slightly that even under prolonged and intense luminous exposure they produce results whichin and of themselves have no practical value in the photographic arts. These purely academic results might have remained scientific curiosities if we had not discovered the cooperating effect of suitable sensitizers which act catalytically or otherwise when incorporated with colloidal coatings. Such coatings are rendered many times more sensitive to light, thusreducing the time in which to secure practical photographic prints ,to seconds which heretofore required :many minutes without atta ning usable results.

The organic materials which we have found available as coatings. in our process are of the most .diverse chemical character. This is so marked that compounds chosen from any of the three general groups of unsaturated organic compounds, generally hydrophobic colloids of the carbocyclic series, heterocyclic series, or the aliphatic series, have been found useful with almost .equally satisfactory results. NVithin these three general series we are not limited or restricted to a particular class of compounds; thusan the aliphatic group the following are instanced as being available for our purpose: hydrocarbons and materials composed 1n whole or in part of such compounds; unsaturated fatty acids, or their salts; esters of unsaturated alcohols or of unsaturated acids, including glycerides', condensation products, or polymerization products, formed by the interaction of aldehydes, ke-

' tones, or acid derivatives, with one another, or with phenols, or with ammonia, amines and related substances.

From the practical results that we have secured, it appears that, in a general way, we may select our materials from any class of organic compounds which are colloidal in nature, or are capable of being changed into a colloidal state by the action of light, providing that such materials are substantially hydrophobic, not easily soluble in water, which differentiates our process from such as used glue, gelatin, and the like substances. However, we do not exclude resinlilre substances such as shellac, guaiacum, etc. In our use of the word hydrophobic, we mean any substances that are not readily soluble in water, but not necessarily the total absence of water.

As examples .of some of the classes which provide available materials for our photographic process, the following are instanced as adaptations:

Garbooyolz'c series. I \Ve have found that unsaturated carbocyclic compounds yield various light-sensitive substances. Certain synthetic resins may be formed by condensing phenols with aldehyde. Such condensation products, however, have little sensitivity to light, but when they are conil 'ned with suitable sensitizers, good prints have been secured in forty-five seconds and less. The reference to times of exposure as herein used are all based on the same source of illumination under identical optical conditions. The details of printing from negatives, etc., are such as are well known in the graphic arts. The source of illumination may be an are light, high power nitrogen incandescent lamps or merwet cury vapor tubes. In an case, for contact printing we may use so id or dry or wet coatings, and for printing by optical projection, we also use fluid, plastic or so-callcd coatings. P -hysical and chemical ohanges take ,place more rapidly in wet coatings than in dry, hence the former are usually the more sensitive.

Among accelerators used for these hydrophobic colloids are lead triethyl iodide, iodoform, mercury alkyls with iodine, and other metallic compounds.

Other resins, such as cumarone, are not appreciably sensitive to light, but this insensitiyeness has also been removed by suitable sensitizers, such as iodoform, with which good prints have been obtained.

In the polyterpene group we have found a number of useful hydrophobic colloids as follows: (a) resins, kauri, etc., which in the case of kanri are scnsitizable by means of iodoform; (b) a caoutchouc colloid may be sensitized by iodo form; and (c) guttapercha can also be made sensitive to light through the use of lead resinate and iodine.

Carbocyc-lic hydrocarbons, such as naphthalene, through condensation yield useful derivatives. Thus, naphthalene and formaldehyde when condensed produce a hydrophobic colloid which when sensitized with iodoform makes a material that is very sensitive to light. In fact, we have made successful exposure in fifteen seconds.

Other derivatives of the carbocyclic series are found in various dyes, such for instance as magenta. In some cases, these show a resinification accompanied by a change of solubility when exposed to 'light; this produces a transformation to a colloidal state and the final product is insoluble in water.

H eterocyclic series.

The heterocyclic class is typified by several groups such as the proteins, the al' kaloids, synthetic resins such as those produced from furfural or pyrrol when condensed with acetone, naphthylamines, and other organic compounds.

The typical protein colloid, blood albumen, was sensitized by means of about 3% iodoform in an alcoholic solution. Under these conditions prints were obtained in about three minutes.

The alkaloida-l substance, nicotine sulphate. diluted with benzol containing about 5% of iodoform, gave a material sensitive to light by projection under an exposure of five minutes.

The synthetic resins derived from monoheteratomic five-membered ring compoundsthe furfura-l, p rrol, thiophene group-by condensation, polymerization or otherwise, are in many cases very sensitive to light in and of themselves, so that additional sensitizing agents are not required.

Thus, a furfural-acetone resin without any sensitizer prints in thirty seconds. Another derivative is furfuramide which, when accelerated with iodoform, produces a print in three minutes. An alcoholic solution of furfuramide may be somewhat diluted by means of water, but the amide is dissolved with difiiculty in water alone. Under the action of light the resinous film approaches 'the state of a hydrophobic colloid. The

condensation product of B-naphthylamine with furfural, when sensitized by iodoform,

Aliphatic series. Among the synthetic products of this series which may be used as colloidal polymers or alternatively when in the mono- 1 series.

molecular state, are the vinyl compounds such as vinyl chloride, or which polymerize in light to a solid resinous film; this change isaccelerated by iodine and it is possible to produce prints on such material in five minutes 1 or less.

Asphaltum appears to be an unsaturated colloidal mixture insoluble in water, possibly derived from hydrocarbons of the aliphatic This material has been known as a light-sensitive medium since 1814, but has not come into neral use on account of its very low sensitivity and the absence of means for greatly increasing'the sensitlvity and simplifying its development. Under the most favorable conditions, the mimmum exposure time heretofore necessary for a. line negative has been twenty minutes. By the use of special'sensitizers, such as iodoform, we are able to produce prints from line negatives on an asphaltum coating in fifteen seconds. I Unsaturated aliphatic hydrocarbon derivatives may be prepared artificially by chlorinating and dechlorinating or other-' wise treating the parafiines; this produces a dark viscous oil or tar that is also of a colloidal nature. In a practical sense it is nonactinic, but we have succeeded in making it responsive to light by adding iodine and lead resinate, thus enabling us to secure an image in about four tofive minutes.

Among the unsaturated aliphatic acids and their derivatives, we have found acids,

salts, and esters that are light-sensitive.- Among the acids, oleomargaric acid becomes thickened when subjected to heat, and after being sensitized with iodine and a metallic salt forms a coating on which prints canbe secured in two minutes. Among the salts we have succeeded in sensitizing lead oleate or leadtungate with iodine so as to produce roducts [prints in one minute. The esters or glycerides, such as perilla oil, tung oiLmenhaden oil, etc., are responsive to varying degrees of luminosity and by proper treatment and, the addition will, when exposed to a luminous image, produce various degrees of solubility in the coating, representative of the image, in a fraction of a second. The foregoing comprehensive list of hydrophobic organic colloids is suflicient to illustrate the' wide vaof cooperating accelerators i riety of such substances available for the purpose of the invention.

Senaz'tz'zers.

In-our use of the designation sensitizers we include materials of a diverse nature, all

of which increase the responsiveness to light of hydrophobm organic colloidal coatlngs. Among various available materials,

we have found that the very important ones o are the halogens, among which iodine is In some cases it can be most adaptable. used in a free state and in other cases compounds of iodine must be used whlch will freely liberate iodine when they are exposed the influence of light in the presence of available oxygen, so as to give up iodine, carbon monoxide, carbondloxide, and: wa-' ter.

gularly activated; in which state it is able to accelerate condensations, polymerization,

halogenation, substitutions, etc., causing selective changes i'nthe structure of the coating under the action of, light which may be permanently fixed by a suitable development of the impressed image. Bromine is also a powerful sensitizer, and in some cases when bromine and iodine are combined and a coatingsensitized therewith, the sensitizing effect is about five times that of the iodine alone.

There are other materials which greatly increase the efiiciency of the haloid sensit-izers. These may be considered as auxiliary accelerators. 'Chief amongthem are compounds of several metals and the or ganic salts are most conveniently employed. These 'may comprise resinates, olea-tes. etc. The useful metals are those whose halides are insoluble in the medium and which are poly-valent, e. g., lead, mercury, nickel, cop per, cobalt, etc. Phosphorous has an accelcrating effect and flourescent dyes, such as rhodar'nine 6G, pheno safranino, etc., also increase the sensitivity. In other cases, notably with the unsaturated glycerides, traces of picric acid cooperate mostefi'ectivelywith the halides to increase their sensitivity.

Minor accelerators, such as solid'oxides,

halides, carbonates, etc., may be used. Such Iodine, when exposed to light, is sinnot specifically claimed herein.

Development.

In the use of our process the technique of .development is probably .purely physical. The developers are chosen for different substances used as coatings so-as to take advantage of the changes produced in the i3 coatings through the .{lCtlOIl of light. These changes are all of a selective order. They appear to be due to variations inviscosity, solubility, porosity, absorptiveness, etc. The image may be made visible through the removal of those parts of the coating that have not been acted upon by the light, or vice versa, through the removal of these parts which have .been acted upon by the light, or through the selective absorption ofsuitable stains, dyes, etc., without the removal of any of the coating.

The variations described above produced selectively by a luminous image in our coating may be taken advantage of by development in several ways. When. the coating changes from a sol, oily, viscous or tacky condition to a gel, plastic or hard solid state, then the image may be developed in the case of an oleaginous coating by simply washing it with soap .and water or, alternatively, by placing atransferring surface in contact with the exposed plate; on itsremoval, there is found on it the soft imprinted areas of here thereon. Under solubility changes, we include reversibility which implies that our colloidal coating has become inversely selective to a specific solvent. Development on this basis consists,'in its-simplest form, in immersing theexposed plate in suitable baths, e. g., a print with a fur- -i:'ural-acetone coating is developed by bathing it in a mixture of turpentine. and benzol, and subsequently rinsing :it with water.

IVith certain coatings, such as bitumen, it

is found desirable to use more or less abrasion. This is usually done by gently rubbing on oleic acid solution over the exposed surface. It is also possible to lay absorbent paper over a print and apply a solvent to the back of such paper when the soluble portions of the image will be taken up selectively by the capillarity of the paper and the remaining portions of the print may be treated in any desired manner.

the coating which ad-' In some cases printed films composed of certain colloidal coatings are not easily developed by solvation; but these show a marked degree of absorption for dyes, taking up 'color from a cooperating dye with which the exposed image is washed. This absorption is selectively proportional to the action of the light to which the coating has been exposed. Among such dyes, we :have found a solventnaphtha oil red stain 'to :be available for this kind of development.

Our coatings, after exposure 'to luminous images, are usually found to be selectively permeable or to have a selective porosity, so that a metallic plate to which the coating is applied can be etched in variable relief approximately proportional to the variation in light and shade of the image. By .reason of this fact, an acid reagent will more quickly reach the metallic sunface beneath the coating where such coating is quite porous. Because of this difference in time when certain parts of the plate are first attacked b the .acid, the etching will produce a variab e relief surfacewithout the dots, lines, etc., if a continuous unbroken change in relief is desired. On the other hand, if such an etching is desired for photo or rotogravure purposes. then intersecting lines, on the completed plate may be used. These serve to assist in holding ink against remova l when the surplus is wiped off before printing.

This porosity is true of most unsaturated colloidal coatings. In some cases a certain solvent, in a selective manner, will only develop the image by the physical removal of the coating; while another solvent frequently produces development only .through selective porosity by a differential effect on the surface to which the coating is ap- .plied, or by a variable change in the coating itself.

As instances of adaptation found to successfully o crate with the unsaturated group of hydrop obic organic colloids, We present the following as exemplifications only and not as limitations. These relate to derivatives which are mentioned in the same order as that to which they have been hereinbefore referred.

In addition to the previously mentioned exemplifications,we have also found the following to give good results. These are not, in anysense, limitations, but are, instead, instances of the adaptability of our process. They relate to the carbocyclic, heterocyclic and aliphatic series of compounds.

In the car'bocyclic series, We have used 12 grams of phenol, 30grams formalin and 2.7 grams of sodium acetate which were mixed together and heated to about 150 degrees 0., for approximately four and one-half hours. The resulting product is decanted and dried. A solution of this resin-like substance wasv sensitized with 2% iodine in benzol,-or with lead triethyl iodide, .or alternatively with iodoform. Coatings of this material produced prints in three minutes or less which were developed in alcohol and water.

' In another exemplification we have used 30 grams of formalin and 20 grams of B- nap ithylamine to form an addition product at room temperature. 20 grams of the dried precipitate was dissolved in acetone to make a 20% solution. When this was sensitized with grams of iodoform, we produced I prints in fifteen seconds.

An additional exemplification, using naphthalene and formaldehyde, was carried out as follows: 100 grams of naphthalene was mixed with 80 grams of formalin and 120 grams of concentrated sulphuric acid. This was heated for three hours in a reflux condenser and the resulting resin was washed with water and a caustic soda solu-- tion. A 20% solution in benzol was sensitized with 5% iodoform which resulted inia thirty minutes producing a resinous'product that is itself sensitive to light to such an extent that prints are produced in thirty seconds.

In an additional exemplification, we have used 100 grams of fur fural mixed with 100 grams of concentrated ammonium hydroxide at room temperature or with slight heating. This produced a resin which, when dried and dissolved in benzol, was of itself sen sitive enough to give prints in five minutes, but when sensitized by means of iodine, iodoform, ammoniumdichromate, etc., produced prints in about half. the previous time.

Inthe aliphatic series, We have found that vinyl benzene, when subjected to steam distillation with storax, produced a dis tillat'e, which, when combined with benzol to form about a 15% solution, was suflicient- 1y self sensitive to produce a print by projection'in ten minutes; but when sensitized with iodine, prints were procured in three minutes.

In another exemplification, we have used asphaltum 10%, solvent naphtha 40%, how zine 25% and sensitizer25%. The sensitizer is made by mixing ethyl methyl ketone 22%, iodoform 12%, .solvent naphtha and concentrated ammonium hydroxide With this procedure, we have successfully produced good prints in fifteen seconds.

We have found, also, that the following exemplification of another aliphatic derivative of the esters produces practicalresults, on coated brass, .1n forty seconds; and in twenty seconds on aluminum. In this ex emplification the following ingredients were used; tung oil 22.7%, lead resinate 1.35%,

lead triethyl iodide 9.1%, iodoform 1.35%,

benzol 44% and solvent naphtha 25%. The 1 iodoform sensitizer, which is added after the addition of the colloid base, produces a mixture devoid of free iodine. It is very sensi tive to light, under the influence of which,

it decomposes rapidly, precipitating lead lodide.

' The coating to which the above'sensitizer is added constitutes a varnish-like substance of tung oil, lead 'resinate, and asolvent. This oil varnish is added to the solution of the lead triethyl iodide in benzol, and the iodoformjs dissolved in this mixture. The advantage of the above sensitizer consists 1n the absence of free iodine, which, by pre venting the areas that are unacted upon' by the light from becoming insoluble, re

sults in prints of great clearness and maximum contrast, without sacrificing the required tonal gradations. As an example of the relation of exposure to areas, we have found that an increase] of 4.8 in area requires an addition of 1.33. inexposure, starting with an area of 1 and, an exposure of 1. An increase of area to 10.2 only increases the exposure to 2, and

a further increase of area to 150 only raises the exposure to 9, which is of great practical value in making enlargement'siof any kind forlithographic posters, etc.

We are unable to state, and the literatureon thesubject issilent regarding, the theoretical explanation of many of the reactions which take place in the practiceof gur process. Whatever divergence there may e between any theoretical hypothesis that we have advanced and any ultimate determination of authenticated technique, reactions,. etc., relating to the same, we doznot limit ourselves to any hypothesis that has been used, for the reason that the practical-dis closures we have made lay the necessary, ground for protection in the, realm of or ganic compounds instanced herein.

In previously filed applications, 'to which wewa-re parties, there have been described,

more in detail, numerous examples 5 which are set forth in the presenhapplicatib and additional examples, also, have'b t, given in the previous applications. This pf plies to the use of various hydrophobic c'ol f loi-ds which are capable of being trans formed under the selective action of light, with subsequent development of the forthe accelerating agents,

in previous applications, there have Also,

of special been given illustrations of the use solvents in many special cases.

In the present application, wehave'heretofore made mention of the use of various solvents, including alcohol, benzol (ben zene), acetone, ketones, benzine, solvent naphtha, and mixtures of such solvents. Among the solvents mentioned, benzol and solvent naphtha are examples of aromatic hydrocarbon. solvents, derived chiefly from coal tar products. especially, in the media and. processes here.- in described. For example, benzol,. solvent naphtha, or a mixture of these materials, af-' fords a solvent; medium which is a. common. solvent for the hydrophobic colloids and vention; employs. Thus, by way of specific example, benzol is a solvent for these hydrohobic colloids and. also is a solvent for 'iodoform, iodine, etc.;. and, as. has been indicated, the halogen-supplying sensitizers are theones which. have been found most usefulv It is; desirable that. the solvent. employer;- ian shall not onl be capable of. dissolvin holding in so-ution the hydrophobic co loids and the sensitizer, when employed, buttne solvent should also befsuchias to produce a solution. which can be freely flowed, or whirled; upon. a suitable surface, not result in streaks, which willlargely evaporatewithina short per'od,.and which willyield a tenaciousand, resistant uniform film capable of being readily. printed and developed. Also, it is desirable that the sol? vent shall be inexpensive and readily. procurable on. the market. The aromatic hydrocarbon solvents, and especiallyy benz ol,

fulfill; in a remarkable degree,.the requirements. It may be-added-that. while lessde sirablesolvents may be employed. in. some. cases, it is advisable, where possible, to em ploya solvent in which the sensitizing agent. will-not decompose. For. example,.while al cohol may be usedin somecasesto-place iodoformin solution, there is danger that. iodoform will-decompose whenin alcoholic solution,.even-in the dark. Thisis trueto some extent of the ketones,,including ace.- tone and,ethy l methyl ketone. For reasons of this kind, it isdesira-ble to employ sol .vents of the aromatic hydrocarbon. class, such-asbenzol, solvent naphtha,.or av mixture of these materials It may be added that when the-most suitable solvent isemployed, a small quantity. of the solvent is strongly, adsorbed by, and remains in the-coating indefinitely, and the quantity solvent influences, markedly, the character of the coating, its speed of printing, and its capability of being developed. Benzol, for. example, possesses this property to a very Such solvents are useful,

which the. in-- which will.

and character of this. remaining.

strong degree, while alcohol, for example, ossesses such pro erty in a very minor egree. That is, t e tendency of alcohol, or similar solvents, is to evaporate almost completely from the coating, and leave a more or less friable coating, which is less, desirable than the tenacious coging which results when benzol, for example, is used. These remarks apply more particularly. to the hydrophobic colloids which we have thus far found to be most desirable for use-in the improved media and processes, but it is to be. borne inmind that other solvents, such asthe ketone, alcohol, or other solvents, may serve useful purposes in special instances.

- The foregoing description has-been given for-clearness of. understanding only, and nounnecessary limitations should'be understood therefrom, but. the a pended claims should be construed as broadly as permissible.

What we regard as new, and. desire to sea cure by, Letters Patent,.is:

1. The process of. preparing a photographic medium which comprises: combining witha. synthetic resin hydrophobic colloid capable of transformation by the selectiveaction of light a solvent medium com-- prising an aromatic hydrocarbon solvent.

2..The process of preparing a photographic medium which comprises: combining with an artificial hydrophobic colloid capable of transformation by the selective action. of light, a solvent medium comprisingbenzol and solvent naphtha.

3. The process of preparing a photo-- graphic medium which comprises: combining with a hydrophobic colloid capable of. transformation under the selective action of light an organo halogen-liberating sensitizer and. a solvent. medium comprising an arbmatic hydrocarbon solvent.

4. The process of preparing a photographic medium which comprises: combinmg. with a hydrophobic colloid capable of. transformation under the selective action of light an organo halogen-liberating sensitizer andia solventmedium comprising benzol.

5.. The. process of' preparing a photographic medium which comprises: combinmg with a hydrophobic colloid capable of transformation under the selective action-of light. an organo halogen-liberating sensitizer and a. solvent medium comprising benzol andsolventnaplitha.

6. The process of preparing a photographic medium which comprises: combining-- witha hydrophobic colloid-capable of transformation under the selective action of light a sensitizer comprising a halogen-substituted hydrocarbon and a solvent medium comprising an aromatic hydrocarbon solvent.v

7. The process of preparing. a photographic medium-which comprises: combining with a hydrophobic colloid capable of transfor- -9. The

mation under the-selective action of light a prises: acting selectively with light, in acthetic resin transformation under the action of light, as-- sociated with a solvent medium comprising cordance with a luminous image, design. or character, upon a coating comprising a synhydrophobic colloid capable of an aromatic hydrocarbon.

11. A photographic process which comprises: acting selectively with light, in accordance with a luminous image, design or character, upon acoating comprising a synthetic resin hydrophobic colloid capable of transformation under the action of light, associated with a solvent medium comprising benzol and solvent naphtha.

12. A photographic process which C0111- prises': acting selectively with light, in accordance with an image, design or character, upon a coating comprising a hydrophobic colloid capable of transformation under the action of light, an associated halogen-liberating sensitizer, and a solvent medium comrisin an aromatic l1 'drocarbon solvent.

13. A photographic process which com pmscs: acting selectively w th light, in accordance with an image, design or character,

"upon a coating comprising a hydrophobic colloid capable of transformation underthe action of light, an associated halogen-liberating sensitizer, andca solvent gnedium com-' prising benzol.

14. A photographic process which comprises: acting selectively with light, in ac cordance with an image, design or character, upon a coating comprising a hydrophobic colloid capable of transformation under the action of, light, an associated halogenliberating sensitizer, and a solvent medium- .COIXIPIlSlng benzol and solvent naphtha.

15. A photographic process which com 1 prises: acting selectively with light, in accordance with an image, vdesign or character,

upon a coating comprising a hydrophobic colloid capable oftransformation under the action of light, a sensitizing agent comprising iodoform, and a solvent-medium comprising an aromatic hydrocarbon solvent.

16. A photographic medium comprising i a solution of a synthetic resin hydrophobic colloid capable of transformation under the action of light and a solvent medium comprising benzol." 17. A photographic medium comprising a solutionof of transformation under the action of light and a solvent medium comprising benzol comprising a halogen-liberating compound, a medium compris ng an aromatic and hydrocarbon solvent.

20. A photographic medium comprising a hydrophobic colloid capable of transformation under the actionof light, a se'nsitizer comprising a'jhalogen-liberating compound, and a solvent comprising benzol.

a hydrophobic colloid capable 7 21. A photographic medium comprising a hydrophobic colloid capable of transformation under the action of light, a-sensitizer comprising a halogen-liberating compound, and a solvent comprising benzol and solvent naphtha.

.22. A hydrophobic colloid capable of transformation under the action of light, an organo halogen-liberating sensitizer, and a solvent medium' comprising an aromatic hydrocarbon solvent. a

23. A photographic medium comprising a hydrophobic colloid capable of transformation under the action of light, a sensitizer comprising iodoform, and a solvent medium comprising an aromatic hydrocarbon solvent. 24. A photographic mediumcomprising a hydrophobic colloid capable of transformation under the actionof light, a scnsitizer comprising iodoform, and a solvent comprising benzol. v

25. A photographic medium comprising a hydrophobic colloid capable of transformation under the action of light, a sensitizer photographic medium comprising a ing benzol and solvent na htha. 26. P

A photographic print comprising a hydrophobic colloid associated with a sensitizing agent comprising a halogen; and a solventmed um comprising an aromatic hydrocarbon solvent, said hydrophobic colloid embodying an image, design or character.

In testlmony whereof we 'aflix our signatures.

MURRAY 0. BEEBE: ALEXANDER MURRAY. 

